1. Field of the Invention
The invention relates to polymeric viscosity index (V.I.) improvers--dispersant additives for petroleum oils, particularly lubricating oils. These additives comprise a copolymer of ethylene with one or more C.sub.3 to C.sub.28 alpha-olefins, preferably propylene, which have been grafted with acid moieties, e.g. maleic anhydride, in a solvent, preferably lubricating oil, and then reacted with a mixture of a branched acid component, and a polyamine having two or more primary amine groups. Or the grafted polymer may be reacted with said branched acid component prereacted with said polyamine to form salts or amides, and then reacted with said grafted olefin polymer. The invention also relates to processes for preparing the preceding products and their use in oil lubricating and fuel compositions.
2. Prior Disclosures
The concept of derivatizing V.I. improving high molecular weight ethylene copolymers, with acid moieties such as maleic anhydride, followed by reaction with an amine to form a V.I.--dispersant oil additive is known in the art. The use of a second acid, e.g. to inactivate primary amine groups, has been found useful as an additional step as indicated by the following patents.
U.S. Pat. No. 4,137,185 teaches reacting C.sub.1 to C.sub.30 monocarboxylic acid anhydrides, and dicarboxylic anhydrides, such as acetic anhydride, succinic anhydride, etc. with an ethylene copolymer reacted with maleic anhydride and a polyalkylene polyamine to inhibit cross linking and viscosity increase due to further reaction of any primary amine groups which were initially unreacted.
U.S. Pat. No. 4,144,181 is similar to U.S. Pat. No. 4,137,185 in that it teaches using a sulfonic acid to inactivate the remaining primary amine groups when a maleic anhydride grafted ethylene-propylene copolymer is reacted with a polyamine.
U.S. Ser. No. 260,883 filed May 6, 1981, now published as European Patent Application 82-302326.2, and U.S. Pat. Nos. 4,144,181 and 4,137,185, used hydrocarbyl substituted succinic acid or anhydride, or long chain monocarboxylic acid, together with the polyamine, and maleic anhydride grafted ethylene copolymer.
The early patents such as U.S. Pat. Nos. 3,316,177 and 3,326,804 taught the general concept of grafting an ethylene-propylene copolymer with maleic anhydride and then reacting with a polyalkylene polyamine such as polyethylene amines. Subsequently, U.S. Pat. No. 4,089,794 was directed to using an oil solution for free radical peroxide grafting the ethylene copolymer with maleic anhydride and then reacting with the polyamine. This concept had the advantage that by using oil, the entire reaction could be carried out in an oil solution to form an oil concentrate, which is the commercial form in which such additives are sold. Subsequently, in operating at higher polyamine levels in order to further increase the dispersing effect, increased problems occurred with the unreacted amine groups cross-linking and thereby causing viscosity increase of the oil concentrate during storage and subsequent formation of haze and in some instances gelling. Even though one or more moles of the ethylene polyamine was used per mole of maleic anhydride during imide formation, cross-linking became more of a problem as the nitrogen content of the polymers was increased. One solution was to use the polyamines and then to react the remaining primary amino groups with an acid anhydride, preferably acetic anhydride, of U.S. Pat. No. 4,137,185 or the sulfonic acid of U.S. Pat. No. 4,144,181, or the succinic acids or anhydrides, or mono-acids of Ser. No. 260,883.
Still another problem arose when using free radical initiators with mineral oil as the grafting medium in that as the grafting levels were increased to increase the dispersancy level, a larger proportion of the oil molecules in turn became grafted with the maleic anhydride. Then upon subsequent reaction with the amine these grafted oil particles tended to become insoluble and to form haze.
The present invention permits the utilization of the generally less expensive polyalkylene polyamines having two primary amine groups, while achieving good dispersancy levels, inhibiting cross-linking and allowing initiator, e.g. peroxide, grafting in oil. A further improvement over the invention of Ser. No. 260,883 (whose disclosure is hereby incorporated in its entirety) is obtained in low temperature viscosity, which is beneficial in making it easier to crank the vehicle engine in cold weather in order to start the engine. The preceding can be obtained by reacting the polymer grafted with the maleic anhydride with a branched chain acid component, having 2 to 6 branches of 10 to 18 carbons each, together with the polyalkylene polyamine, e.g. polyethyleneamine. Cross-linking between ethylene copolymer molecules is reduced or inhibited since many of the polyamine molecules will have one primary group reacted with a maleic anhydride moiety of the ethylene copolymer, while its other primary group is reacted with the branched chain acid component. A further advantage is when the grafting is carried out in an oil solution, using a free radical initiator, e.g. a peroxide which is generally much faster with better control, than say depending upon thermal cracking or degradation, oil molecules which become grafted with maleic anhydride and react with the amine, will, to a substantial extent, be solubilized.